Two different studies on this page - with very similar information

Teenage media habits survey July 2010

http://www.businessinsider.com/the-shocking-media-habits-of-8-18-year-olds-2010-7

2000 families

Basically, if kids are awake, they're consuming media.

Following are some of the results

See VitaminDWiki

• Every hour of TV watched reduces your lifespan by 22 minutes – Aug 2011

• 43 reasons for Vitamin D deficiency

• Dark skinned teens use media much more - June 2011

That web page has the following graphic